Heat pipes provided with a wick have been developed, and wick materials of various shapes are known, such as gauze-like materials, fibrous materials, and porous materials. In such a heat pipe, vapor from a working fluid travels in a specific direction of the pipe, and a condensate liquid of the working fluid is refluxed in the opposite direction through capillary action. This evaporation-condensation cycle repeats. However, for such heat pipes provided with a wick, there is the problem of a limit on emission of a refluxed working fluid due to working vapor.
To solve this problem, various proposals have been made for the structure of a heat pipe provided with a wick.
For example, Patent Document 1 discloses a flat heat pipe having a grooved wick on its inner wall and having a flat cross-sectional shape, wherein at least one linear auxiliary wick extending along the axis is disposed at both inner ends of the flat cross-section in the width direction.
Patent Document 2 discloses a heat pipe including a working fluid that is filled in a container and repeats evaporation and condensation, and a thin wick configured to transfer the working fluid from a cooling end to a heating end, wherein the wick is disposed along and near/abutting the inner wall surface of the container; innumerable groove-like passages are formed on at least a side opposite to the inner wall surface of the container along the direction from the cooling end to the heating end; and the outer sides of flat portions of the wick are hydrophilic treated.
Unfortunately, according to the techniques disclosed in these prior art documents, when the relative velocity between a vapor flow and a working fluid in a wick is high, an emission limit is reached where some emissions from the working fluid do not return to an evaporation unit, resulting in a low maximum heat transfer rate.